According to incomplete statistical data, the transportation amount of municipal domestic waste in China in 2014 was 178,600,000 tons; the domestic waste treated in a sanitary landfilling way which was effective to treat the municipal domestic waste was 107,440,000 tons, with 60% in total disposal ways. But the moisture content of mixed waste landfilled in China was as high as 40-60%, which was far greater than 20-30% in European and American countries. Moreover, domestic kitchen waste had a relatively high content of organic matters 60-65% in total domestic waste), and after being landfilled, the waste in itself was compressed and degraded to generate a large amount of leachate (landfill leachate) and landfill gas. However, the direct landfilling of the waste is easily inhibited by a highly concentrated organic acid; the methane-producing process is delayed; and under the conditions in which the diversion of rain and sewage water is improperly operated, the guiding-discharging designed capacity is low or a guiding-discharging facility is blocked, the landfilled waste is easily formed into a water barrier layer, such that the infiltration of the leachate is hindered and the leachate cannot be guided and discharged, even the water level of the leachate is raised, and thus the effective collection of the landfill gas is affected and there exists an environmental safety risk.
At present, due to a fact that most of waste landfills in China have low treatment technological level or improper management, there are problems such that a large amount of the landfill gas is released in an unorganized manner, the landfill gas is leaked and exploded the water level of the leachate is raised, the leachate is leaked and diffused, and the waste pile is in sedimentation deformation and out of stability. With the exploitation and utilization of the landfill gas, the internal pressure of the waste body may be reduced and the landfill gas therein is prevented from gathering to cause a fire, an explosion and other accidents. Therefore, in order to guarantee the safe operation of the waste landfill, there is a need to effectively control the landfill gas and the leachate therein.
Currently, it is a common practice for most waste landfills to compact the waste in a layered manner and cover it every day. In such a way, an operation side is sealed difficulty, such that the landfill gas is collected in an existing manner of drilling and erecting a vertical gas extraction well or a gas collecting pipe after the waste landfill is closed. Under the conditions in which an air seal is damaged or is submerged by the high-level leachate that is difficult to be discharged in time to form a water seal due to non-uniform waste settlement, it is easy to cause non-effective gas extraction or even paralysis. As a result, the landfill gas collection efficiency is extremely low. Furthermore, once excessive landfill gas is piled in the landfill, the pore pressure of the landfill is increased and therefore there exists a huge potential safety hazard to the landfill. Meanwhile, the leachate in the waste landfill is collected using an existing bottom leachate converging system, so under the conditions such as the pipe is deformed, blocked or corroded once the leachate cannot be guided and discharged out in time, the water level of the leachate is raised easily, and thus the landfill gas collection efficiency is reduced. Besides, there are more rains in south and has a turbulence phenomenon of a gas recycling pipe network commonly confronted by the waste landfill that the water level of the leachate is relatively high in essence, and after the rainwater is infiltrated from a surface of the landfilled waste, the water level of the leachate inside the waste is raised and the gas extraction well is blocked; and therefore, the discharging and the recycling rate of the landfill gas are directly affected.
Therefore, how to work out a gas-liquid controlled collection technology with high landfill gas collection efficiency, and smooth leachate guiding and discharging on the basis of existing landfill gas and leachate collection technologies and by combining with the characteristics of the landfills in China is of a great significance.